Setting OAF Pressure Gauges

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Hello,I read somewhere how to set OAF pressure gauges without referring to the dials of the gauges themselves.  This was described as an old aviation industry trick.I have searched the archives and can not find this info.  It may not even have been on this forum.  I thought it may have been on the Tin Mans website,  http://tinmantech.chainreactionweb.com/ , but can not find it there.If you can help I thank you.Bob
Reply:Hello again,I just answered my own question.  The info was on the TM Technologies site (The Tin Man).  http://tinmantech.chainreactionweb.c...ch_setting.php
Reply:Interesting technique.  What's wrong with just knowing where to set the regulators?  Seems faster, but maybe I'm missing something?By the way, the process is OF-A, not OAF. (Oxygen-Fuel - Acetylene)
Reply:Originally Posted by MAC702Interesting technique.  What's wrong with just knowing where to set the regulators?  Seems faster, but maybe I'm missing something?By the way, the process is OF-A, not OAF. (Oxygen-Fuel - Acetylene)
Reply:Out of curiosity, when you adjust it by feel, what does the gauge say, or is it still pegged on the bottom?I'm sure your method will work, and I'm not trying to tell you someone's full of it; I'm just exploring this idea a little.
Reply:Originally Posted by MAC702Out of curiosity, when you adjust it by feel, what does the gauge say, or is it still pegged on the bottom?I'm sure your method will work, and I'm not trying to tell you someone's full of it; I'm just exploring this idea a little.
Reply:I use to adjust my o/a torch by fully opening the acetylene valve at the torch.  Then, I would adjust the regulator until the flame jumped away from the torch then I reduced it a little.  I would get a neutral flame the same way --open torch o2 torch valve completely, then adjust the regulator until I got a neutral flame.I did it because I was trying to weld and got frustrated.  I didn't have any charts for my torch tips.  I figured that method would give the max pressure at the tip and I make adjustments at the torch.
Reply:Adjusting pressures with the regulators and adjusting flows with the needle valves are not interchangeable ways of doing the same thing.The pressures are set based on the tip being used and are set at various ratios to one another, usually based on who taught you to do it.The needle valves are for adjusting the flame for neutrality or other properties.Sounds like you know this, but just needed to get it done the other way for some reason, but I just didn't want a new person to try that as a standard procedure.
Reply:Hey MAC702,I just found another source for the regulator setup that is nearly identical to the one discussed above.I don't think I am allowed to copy this info directly hear so I will include the link.The post is #6 by Northweldor. http://www.aws.org/cgi-bin/mwf/topic...l=oaw#pid31337
Reply:Why do we need tricks to set O/A guages?  It's almost always 7 psi on the acetylene.  When welding, I just run the O2 a little higher than the acetylene.  When cutting, 35 psi covers almost everything that we will ever do.  Some larger tips take up to 60 psi, but that's for 12 inch thick steel.  Most of the time, I run the O2 reg at 35 psi regardless of whether I'm cutitng or welding because I can fine tune the pressures in the handle.If it bothers you, the manufacturers provide pressure settings for every tip.  Look it up.
Reply:Mac you're ablsoutely right about adjusting the valves on the torch for flame adjustment.My reasoning for adjusting the the regulators was to get in my opinion the max acetylene pressure for the given tip and close with the oxygen.  I then adjusted the flame from a crack to wide open.  The symptom- I was getting a lot of torch pop.        With oxygen pressures set really high there in not much fine tune-ability especially for smaller welding tips.  76gmc you must have a couple of favorite welding tips.I personally was never sure what the actual drill size of my tip.  That is one reason one might resort to tricks.
Reply:Originally Posted by 76GMC1500Why do we need tricks to set O/A guages?  It's almost always 7 psi on the acetylene.  When welding, I just run the O2 a little higher than the acetylene.  When cutting, 35 psi covers almost everything that we will ever do.  Some larger tips take up to 60 psi, but that's for 12 inch thick steel.  Most of the time, I run the O2 reg at 35 psi regardless of whether I'm cutitng or welding because I can fine tune the pressures in the handle.IF it bothers you, the manufacturers provide pressure settings for every tip.  Look it up.
Reply:My reasoning for adjusting the the regulators was to get in my opinion the max acetylene pressure for the given tip and close with the oxygen.
Reply:I believe there is a lot of misconception about what exactly is going on with the settings.  When you set a regulator to the manufacturer recommended pressure, all you are doing is ensuring you'll have sufficient gas flow to the torch.  The needle valves on the handle are what set the pressure at the tip which is significantly lower than the regulator pressure.  If the manufacturer states 7 psi for a tip, as long as you have 7 psi in the hose, you will have sufficient gas flow.  If you run more pressure, you'll just have to open the valve on the torch handle a little less, but there will be no effect on the final and balanced flame.  Running your regulators closer to the recommended/minimum pressures does give you a better ability to fine tune the flame.  With my O2 reg set at 35 psi, I have absolutely no problem achieving the flame balance I want, so I don't bother fiddling with the regulator.  If the valves on your handle are touchy, you may want to run lower pressures.
Reply:Originally Posted by 76GMC1500...The needle valves on the handle are what set the pressure at the tip which is significantly lower than the regulator pressure....
Reply:But who runs their torch in an enclosed system?  You're just complicating things here.  Besides, flow and pressure are interelated.  In your same system, as the pressure in the tank approches the regulator pressure, the flow will approach 0 even though the valve position remains the same.  So, the valve doesn't really set the flow, either.
Reply:There is a fundamental difference between flow and pressure, even though one affects the other.I'm only bringing it up because you clearly stated the needle valves were adjusting pressure, which they most certainly are not.  THAT would be complicating things.Many types of valves, including gate and needle valves are designed to adjust flow.Like you say, they NORMALLY do so in an open-ended system, which is how they maintain a CONSTANT flow per valve position.  Even in a changing pressure system, the valve will still adjust FLOW (and not pressure), it will just be a changing scale as pressure also changes.Needle valves adjust flow, end of story.
Reply:You can argue that they control the pressure drop or that they control the flow, but there is really no reason to argue it here.  In fact, there is really no reason to argue it anywhere.
Reply:An argument is an exchange of opinions.  There is no opinion possible on whether a needle valve adjusts flow or pressure.  It adjusts flow.  However you choose to visualize that adjustment for yourself is fine, but all I did was clarify the proper terminology, just like I stated at my outset; it was never an argument.Last edited by MAC702; 06-04-2007 at 09:13 PM.
Reply:I think I'll make a meager attempt to complicate things further. Lets say you turn your oxy regulator up to 35 psi and compensate for the higher pressure by opening the needle valve less. I can see how it is certainly possible to achieve the same mass flow of oxygen as if the regulator were set to 5 psi with the needle valve open more. My question is what effect would this have on the velocity of the oxygen flowing to the tip, and how if at all, would that affect the flame?Miller EconotigCutmaster 38Yes ma'am, that IS a screwdriver in my pocket!
Reply:Compensating the pressure by adjusting the flow.  It would certainly work within an acceptable range, because that's what it already does.  The pressure setting is never PERFECTLY consistant or efficient, so that's exactly why we have needle valves instead of a ball valve.  But, the way you put it, Joe, makes it easier to visualize.  I like to look at the extremes of a situation just to help see how the typical situation reacts to stimuli.The more the pressure at the needle valve, the closer the needle valve would be to shut during optimum flow and the harder it would be to make small adjustments.The less pressure available at the valve would mean the valve would be more open for optimum flow, but too little pressure and a fully open needle valve would still be a constriction in series with the hose and fittings and torch.There's a happy medium for needle valve supply pressures, and it's found somewhere around the pressures recommended by the torch manufacturer.Now, Joe, I have no idea at what point the needle valves (by adjusting the flow) can no longer efficiently deal with increasing supply pressures, but it's maybe somewhere close above your numbers.  I've never tried to find out, but it's a good question.
Reply:It's incorrect to think of a valve as controlling only flow.  There are 3 factors pressure differential, area, and flow.  If you know two, you can calculate the third.  Pressure and flow are interrelated and should not be thought of as seperate things.  In some situations, especially in an open system, they can be used interchangeably.Joe, when running high O2 pressures on the regulator, yes the velocity of O2 is higher in the valve.  But, the mixing tube of the torch has a large volume and the gas velocity quickly reduces in the handle of the torch.  So, the velocities at the tip are the same regardless of the pressures at the regulator.
Reply:Valve: any device for halting or controlling the flow of a liquid, gas, or other material through a passage, pipe, inlet, outlet, etc.  (From www.dictionary.com)Needle valve: a type of valve having a small orifice and a threaded, needle-like plunger. It allows precise regulation of flow, although it is generally used for, and is capable of, only relatively small flow rates.  (From www.wikipedia.com)Compare those with your dictionaries and get back to us.Just because things are in a cause-and-effect relationship most certainly does NOT mean the terms are interchangeable.  If you continue to think that, there's no place left for me to reason with you.PS, none of this is personal.  You're a swell guy.  But I'm maintaining that you are dead wrong here.
Reply:double post, please delete, since I'm not allowed to.
Reply:I noticed a difference when I used to weld with o/a.  If he pressure is too high then it was difficult to adjust the flame.  Also, the weld puddle blew around to fast for me to comfortably control.  That is it exact reason I used the method I described above.  I add the full range of knob control to adjust the gases.Also, I read the acetylene torch valve should be opened 3/4 to 1 full turn  prior to lighting.  If oxygen pressure is too high it is just plain difficult to adjust or maintain a good flame.Originally Posted by MAC702Valve: any device for halting or controlling the flow of a liquid, gas, or other material through a passage, pipe, inlet, outlet, etc.  (From www.dictionary.com)Needle valve: a type of valve having a small orifice and a threaded, needle-like plunger. It allows precise regulation of flow, although it is generally used for, and is capable of, only relatively small flow rates.  (From www.wikipedia.com)Compare those with your dictionaries and get back to us.Just because things are in a cause-and-effect relationship most certainly does NOT mean the terms are interchangeable.  If you continue to think that, there's no place left for me to reason with you.PS, none of this is personal.  You're a swell guy.  But I'm maintaining that you are dead wrong here.
Reply:Originally Posted by MAC702...The more the pressure at the needle valve, the closer the needle valve would be to (the) shut (position) during optimum flow and the harder it would be to make small adjustments....
Reply:Originally Posted by phila.renewal...Assuming an initial state where the needle valve on the torch is fully open, what happens to the pressure behind that valve if you were to nearly close it to reduce the flow?  If the regulator can keep the pressure behind the valve the same, open or not, then I would agree with you.  If it increases then there is some merit to the concept that the valve controls both flow and pressure.My guess would be the pressure stays the same (or nearly so).  A guess...
Reply:Originally Posted by phila.renewal...Now, another thought, lets look at pressure beyond the valve headed for the tip.  Assuming an initial state where the needle valve is nearly closed, what would happen to the pressure beyond the valve if it were opened to increase the flow?  My guess would be the pressure would increase.  Again, a guess.  I don't know the relationship between typical flow rates and the constrictions in a typical torch.  If the pressure did not increase then again, I'd have to give it to you that the valve in question controls only flow and not pressure.Interesting stuff (as always).
Reply:Pressure would increase because you are pushing gases out of the tip, whereas before they were just sitting there in equilibrium with the atmosphere.
Reply:I said it was at equilibrium with the atmosphere BEFORE pushing the gases out of the tip by opening the valve, and exposing it to the regulator's pressure.
Reply:That is not exactly what you typed.  You typed "...they were just sitting...".  That leads me to believe you were refering to Oxygen and Acetylene on the other side of the valve.I'm through with this, later.
Reply:Originally Posted by MAC702Pressure would increase because you are pushing gases out of the tip, whereas before they were just sitting there in equilibrium with the atmosphere. ....
Reply:As long as there is flow through the needle valve, there is a pressure drop through the valve.  So, the pressures at the tip are not the same as the pressures in the regulator/hose.
Reply:Yes, that is true.  The pressure drops through every length of hose and at every fitting, too.  A needle valve in particular is a high-resistance valve.  But you could still say that the pressure in the tip is set by the regulator, it's just at less pressure than the regulator itself.